1. Field of the Invention
The present invention relates to a method of manufacturing a lamp employed for vehicle use such as headlamp, turn signal lamp, or stop-lamp, in which a lamp lens is joined to a lamp body made of synthetic resin.
2. Description of the Related Art
As a method of joining a lamp lens to a lamp body consisting of synthetic resin, the method of fixing these two together by using a adhesive could be employed. However, in view of environmental problems, the so-called hot plate melt-bonding method, in which the lamp body, typically consisting of a thermoplastic resin such as ABS resin, is melted by pressing a hot plate onto it and the molten part is then press-fixed onto a lamp lens consisting of methyl methacrylate resin etc. is becoming more widely adopted since, unlike the method in which fixing is effected using adhesive, it employs no solvent at all. However, with such a hot plate melt-bonding method, there was sometimes the problem that, on separating the hot plate after using the hot plate to melt the thermoplastic resin constituting the lamp body made of ABS resin or the like, the molten resin gets drawn out in the form of a thread (hereinbelow this is referred to as "thread drawing") which adheres to the surface of the molding of the lamp lens or lamp body, adversely affecting its appearance. As a method of improving the situation regarding thread drawing in this hot plate melt-bonding method, for example Early Japanese Patent Publication H. 9-12902 proposes the method of adding a fluorine resin such as polytetrafluoroethylene to the thermoplastic resin such as polycarbonate or ABS resin. However, with this method, the cost of the vehicle lamp that is manufactured is increased and also, since the external slipperiness of fluorine resins is high, if the added amount is large, when the resin is extruded from the extrusion molding machine in extrusion manufacture of the pellets for molding, so-called surging occurs, adversely affecting productivity. Furthermore, secondary processing may be adversely affected in that there may be poor adhesion of the evaporated film or coating when vacuum evaporation is performed onto the inner surface of the molded lamp body or its outer surface is coated.